Load-sensing and pressure-limiting device with accelerated tripping

ABSTRACT

A load-sensing and pressure-limiting device is disclosed for fluid-driven appliances having at least two fluid-driven working motors, in which the load on a first working motor is variable by operating one or more other working motors, wherein a pressure proportional to the load on the first working motor is sensed by the device and used to avoid overloading of the first working motor. The sensing device has a primary piston with smaller cross-sectional area, intended to sense the load on the first working motor, and a secondary piston with larger cross-sectional area, both pistons being displaceable in a cylinder having two slots of different cross-sectional area, corresponding to said area of the pistons, to a tripping position where one or more ports communicating with the fluid pipes of the one or more other working motors are opened, whereby the fluid pressure applied to these other working motors can act upon the secondary piston and move it further in tripping direction.

United States Patent 1 1 Gustafsson et al.

1 1 Dec. 2, 1975 1 1 LOAD-SENSING AND PRESSURE-LIMITING DEVICE WITH ACCELERATED TRIPPING [75] lnventors: Karl Paul Gustafsson; Lars-010v Frisk, both of Gavle, Sweden [30] Foreign Application Priority Data Oct. 5, 1972 Sweden 12892/72 [52] US. Cl. 91/412; 60/426; 91/414; 91/451; 137/115; 137/596.12 [51] Int. C1. F15B 13/06 [58] Field of Search 91/446, 448, 414, 412,

OTHER PUBLICATIONS Hydraulic Handbook, 2d. Ed., Trade and Technical Press, Surrey, England (1960) pp. 144 et seq.

Germany 137/115 Primary E.\'aminerC. J. Husar Assistant ExaminerEdward Look Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT A load-sensing and pressure-limiting device is disclosed for fluid-driven appliances having at least two fluid-driven working motors, in which the load on a first working motor is variable by operating one or more other working motors, wherein a pressure proportional to the load on the first working motor is sensed by the device and used to avoid overloading of the first working motor. The sensing device has a primary piston with smaller cross-sectional area, intended to sense the load on the first working motor, and a secondary piston with larger cross-sectional area, both pistons being displaceable in a cylinder having two slots of different cross-sectiona1 area, corresponding to said area of the pistons. to a tripping position where one or more ports communicating with the fluid pipes of the one or more other working motors are opened, whereby the fluid pressure applied to these other working motors can act upon the secondary piston and move it further in tripping direction.

5 Claims, 1 Drawing Figure 1 4 L T T 1 I I 9 220 5w, 1 I l r7 I \/4. II-. LF+J l8 9' 27 leve US. Patent Dec. 2, 1975 LOAD-SENSING AND PRESSURE-LIMITING DEVICE WITH ACCELERATED TRIPPING FIELD OF THE INVENTION This invention relates to a load-sensing and pressurelimiting device intended for use preferentially for fluiddriven appliances having at least two fluid-driven working motors, the load of a first working motor being variable by running one or more other working motors. A

pressure proportional to the load of the first working motor is sensed by a sensing device and used to avoid overloading the first working motor by another working motor.

DESCRIPTION OF THE PRIOR ART SUMMARY OF THE INVENTION The object of the present invention is to avoid this oscillation and, a load-sensing and pressure-limiting device is proposed which, on attaining the first stage of the tripping position, distinctly changes to marked tripping. This should furthermore be done in a simple and uncomplicated manner and by means of an appliance produceable at low cost.

According to the invention this is achieved chiefly through the use of a sensing device which has a primary piston with small cross-sectional area, intended to sense a pressure proportional to the load of a first working motor, and a secondary piston with a larger cross-section al area. Both pistons, against the force of a spring, are displaceable in a cylinder with two slots of different free cross-sectional area, .the areas corresponding to the cross-sectional area of the pistons. The pistons are movable to a tripping position where two ports communicate with one another, a valve is opened, and the secondary piston, after displacement through the primary piston to incipient tripping position, opens one or more ports communicating with the fluid pipes of the one or more other working motors, which are coupled to functions increasing the load of the first working motor. The fluid pressure applied to these other working motors acts upon the secondary piston and move it further in the tripping direction. In this way an accelerated tripping is obtained which takes place distinctly and without repeated oscillations around the tripping point.

According to a preferred embodiment of the invention it is proposed that one of the pistons should have a slot or the like, that the cylinder should have a port connectable to a fluid pressure source and a second port connectable to an essentially pressureless fluid recipient, and that the relative positions of the ports and of the slot are such that the ports communicate with one another in when the pistons are in the tripping position.

According to a further development of the invention it is proposed also that, in the cylinder, on each side of the secondary piston, there should be chambers which are interconnected by means of a constriction orifice, preferentially in the secondary piston, one chamber communicating with the port of the cylinder which is connectable to the fluid recipient.

According to another development of the invention, in order to prevent the various other working motors from being affected by one another, check valves are placed in the connections between the other working motors and the connectable chamber of the cylinder, to prevent fluid from one working motor from flowing over via said cylinder or chamber to one or more of the other working motors.

To render the device according to the invention usable for various tripping pressures presettable according to the intended application, it is proposed that the spring should be pretensionable by means of a screw device and that the spring be placed in a chamber of the cylinder which is connectable to the fluid recipient.

BRIEF DESCRIPTION OF THE DRAWINGS An application of the invention will now be described with reference to the attached drawing. The FIGURE shows a load-sensing and pressure-limiting device according to the invention in a longitudinal section, in an hydraulic circuit for a fluid-driven appliance having four working motors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The appliance operates as follows. From a pump P hydraulic medium is pumped via a pipe 1 to the various regulating valves V1, V2, V3 and V4. The pressure in pipe 1 is limited by a pressure-limiting valve 0 acting as relief valve. In this case the hydraulic medium is led via a pipe 2 back to a pressure medium recipient T.

To the regulating valve V1 there is connected a first working motor A1. To the other regulating valves V2, V3, V4 are connected other working motors, the driving of which can increase or decrease the load of the first working motor A1 and thus in principle can also bring about overloading of the first working motor A1.

To raise a load by means of the first working motor Al the lever of the regulating valve V1 is moved to the lifting position, whereupon the pressure medium from pipe 1 is led via check valve B1 to pipe 3 and thus to the pressure chamber of lifting cylinder A1. To pipe 3 is connected a sensing pipe 4 running to the union 10 of a sensing valve AV. The latter communicates with a cylinder 28, in which there is a displaceable primary piston 11. The primary piston 11 in turn is connected to a secondary piston 12, which will be described below. If the lifting fluid pressure exceeds a maximum value permissible for the system, thepressure-limiting valve 0 opens and further lifting, and thus increase of the load on the first working motor A1, is prevented by the pressure-limiting valve 0 relieving pipe 1 by leading part of the flow to pipe 2.

If a suspended load is to be lowered by means of an outer boom linked to the outer end of the crane beam, the lever of the regulating valve V2 is moved to lower position and pressure medium is supplied via pipe 1 and the pressure-controlled check valve TBl, pipe 6 and pipe 5 to the second working motor A2. At the same time the second pressure-controlled check valve TB2 is opened via the pressure control pipe, so that hydraulic medium forced out of the second chamber of the second working motor A2 via pipes 8 and 7 can flow back to pipe 2 and the pressure medium recipient T. If the outer boom is in an upward position, a lowering movement will increase the leverage, which will increase also the load on the first working motor A1. When the first working motor Al approaches its maximum permissible load, the sensing valve AV will be so actuated via the sensing pipe 4 that the primary piston 11 is displaced to the left in the FIGURE against the force of the spring 15, which can be tensioned to the desired extent with a screw 16. Through leftward displacement of the primary piston 11, the secondary piston 12 is also displaced to the left. When its right-hand edge 13 reaches edge 14, the pressure applied to the second working motor A2 in pipe 6 is able to be propagated via pipe 9, a union 17 and a check valve BVl to the pressure chamber 18 to the right of the secondary piston 12, whereby suddenly a larger area is subjected to pressure and the secondary piston 12 is distinctly displaced a bit further to the left.

In the middle of the secondary piston 12 there is a peripheral slot 19 communicating with an outlet port 20 which, via pipe 2, communicates with the pressure medium recipient T. Through the said leftward displacement of the piston the left-hand edge 21 of the slot 19 passes the right-hand edge 22 of an inlet port 23 communicating with the pressure pipe 1, whereby the pressure pipe 1 is connected via port 23, slot 19, port 20 and pipe 2 to the pressureless tank T, so lowering the pressure in pipe 1, and thus also the pressure applied via pipes 1, 6 and to the outer boom cylinder A2, the lowering of which is thus limited owing to the falling pressure. This falling pressure is also propagated via pipe 9 to the pressure chamber 18, whereby the pressure forcing the piston to the left diminishes and finally a state of equilibrium occurs, which implies that the load remains at a given angular position of the outer boom without being further raisable or able to sink down of its own accord.

If the lever of the regulating valve V2 is returned to neutral position, no hydraulic pressure is any longer applied to the union 17 and the secondary piston 12 is displaced further to the right through the force of spring 15. At the same time, via a constricting orifice 24 inside the piston an equalization of pressure arises between the pressure chamber 18 and a chamber 25 situated to the left of the secondary piston and communicating via a pipe 26 with the outlet port 20 and thence with the pressureless pressure medium recipient T.

The connection between the port 23 and the slot 19 is shut off since the edge 21 passes the edge 22 in the rightward direction. Thereby the pressure in pressure pipe 1 can rise again and one can, for example, raise the outer boom slightly or continue the lowering with the aid of the lifting cylinder, i.e. the first working motor Al. This is possible without risk of overload as the coupling of the first working motor A1, i.e. of the lifting cylinder, to the crane beam is now usually effected in such a way, that there is practically constant loading of the working motor A1, regardless of the final position of the crane beam, assuming constant load.

In a manner analogous to that described above, raising of the outer boom from a downward-directed position nearer the horizontal can be prevented if the load on the first working motor Al, i.e. on the lifting cylinder, would thereby exceed the maximum permissible.

Overloading of the lifting cylinder A1 can also be adequately prevented by extension of an extension cylinder on the outer boom of the crane beam. In the embodiment shown in the drawing this extension cylinder may be considered to be represented by, for example, one of the other working motors A3. If, in the case of a suspended load, extension takes place by moving the lever of the regulating valve V3 to extension position, the fluid pressure is applied from pipe 1, pipe 6, via the pressure-controlled check valve T83 and pipe 5 to the lower chamber of the extension cylinder A3. At the same time the pressure-controlled check valve T84 is opened, so that via pipes 8' and 7 the corresponding quantity of pressure fluid can flow from the upper chamber of the extension cylinder A3 back to pipe 2 and tank T. As soon as the lifting cylinder A1 attains its maximum permissible load owing to the increased leverage resulting from the extension, the secondary piston 12 has been displaced so far by the sensing pipe 4 and the primary piston 1 1 that the edge 13 has come on a level with or slightly past edge 14. Thereby the pressure applied to the extension cylinder A3 via pipe 9' and union 27 flow through the check valve BV2 into the right-hand chamber 18 of the cylinder, so that the secondary piston 12 is distinctly displaced further to the left and the left-hand edge 21 of the slot 19 passes the right-hand edge 22 of the inlet port 23, so creating a connection between the pressure pipe 1 and the tank T, with the above-described result in consequence.

It is naturally within the scope of the invention to apply it also to servo-controlled systems and servo-controlled working motors, in which case for example the servo control pressure can be connected to the inlet port 23. The protection also covers embodiments in which pistons 11, 12 mechanically, hydraulically or electrically act upon a pressure limiting or relieving device of optional kind.

Through this invention, accordingly, has been achieved a load-sensing and pressure-limiting device with accelerated tripping, which, on reaching the very first stage of the tripping position distinctly changes to marked tripping without disturbing oscillation or hunt What is claimed is:

1. A load sensing and pressure limiting device for a fluid-powered appliance having at least two fluid driven working motors, supplied from a common hydraulic supply line, in which the load on a first working motor is variable by operation of at least one other working motor, wherein a pressure which is proportional to the load on the first working motor is to be sensed and used to avoid overloading the first working motor by the other working motors, comprising:

a. a housing (28) having a first cylindrical recess, a second cylindrical recess, a second hydraulic inlet port (10) communicating with said first cylindrical recess, a second hydraulic inlet port, at least a third hydraulic inlet port, and an hydraulic outlet port, each communicating with said second cylindrical recess,

b. a primary piston slidably retained in said first cylindrical recess,

c. a secondary piston rigidly connected to said primary piston and slidably retained in said second cylindrical recess, said secondary piston having a larger cross-sectional area than said primary piston,

d. spring means interposed between said secondary piston and said housing to normally bias said primary and said secondary pistons in one direction, such that said secondary piston closes said second and third hydraulic inlet ports,

e. first conduit means connecting the hydraulic supply line to said second hydraulic inlet port,

f. at least a second conduit means connecting the at least one other working motor to said at least third hydraulic inlet port such that hydraulic pressure acting on said at least one other working motor is transmitted thereto,

g. third conduit means connecting said hydraulic outlet port to a hydraulic return line, and

h. fourth conduit means connecting said first working motor with said first hydraulic inlet port to transmit the hydraulic pressure acting on said first working motor to said primary piston causing the primary and secondary pistons to move against the spring biasing means to uncover the second and third hydraulic inlet ports thereby causing said hydraulic pressure acting on said at least one other working motor to act on said second piston to increase its movement against the spring biasing means and allowing the second hydraulic inlet port to communi- 6 cate with the hydraulic outlet port to reduce the supply line hydraulic pressure.

2. A device according to claim 1 wherein a circumferential slot in said secondary piston allows communication between said second hydraulic inlet port and said hydraulic outlet port when said secondary piston is displaced from its biased position.

3. A device according to claim 1 wherein a chamber is defined by each end of said secondary piston and the ends of said second cylindrical recess, said chambers communicating with each other via a constriction orifice and passageway through said secondary piston.

4. Device according to claim 1 wherein check valves are placed in the at least third hydraulic inlet port.

5. Device according to claim 1 wherein the spring biasing means is pretensionable by means of a screw device and is placed in a chamber of the cylinder which is connectable to the fluid recipient. 

1. A load sensing and pressure limiting device for a fluidpowered appliance having at least two fluid driven working motors, supplied from a common hydraulic supply line, in which the load on a first working motor is variable by operation of at least one other working motor, wherein a pressure which is proportional to the load on the first working motor is to be sensed and used to avoid overloading the first working motor by the other working motors, comprising: a. a housing (28) having a first cylindrical recess, a second cylindrical recess, a second hydraulic inlet port (10) communicating with said first cylindrical recess, a second hydraulic inlet port, at least a third hydraulic inlet port, and an hydraulic outlet port, each communicating with said second cylindrical recess, b. a primary piston slidably retained in said first cylindrical recess, c. a secondary piston rigidly connected to said primary piston and slidably retained in said second cylindrical recess, said secondary piston having a larger cross-sectional area than said primary piston, d. spring means interposed between said secondary piston and said housing to normally bias said primary and said secondary pistons in one direction, such that said secondary piston closes said second and third hydraulic inlet ports, e. first conduit means connecting the hydraulic supply line to said second hydraulic inlet port, f. at least a second conduit means connecting the at least one other working motor to said at least third hydraulic inlet port such that hydraulic pressure acting on said at least one other working motor is transmitted thereto, g. third conduit means connecting said hydraulic outlet port to a hydraulic return line, and h. fourth conduit means connecting said first working motor with said first hydraulic inlet port to transmit the hydraulic pressure actiNg on said first working motor to said primary piston causing the primary and secondary pistons to move against the spring biasing means to uncover the second and third hydraulic inlet ports thereby causing said hydraulic pressure acting on said at least one other working motor to act on said second piston to increase its movement against the spring biasing means and allowing the second hydraulic inlet port to communicate with the hydraulic outlet port to reduce the supply line hydraulic pressure.
 2. A device according to claim 1 wherein a circumferential slot in said secondary piston allows communication between said second hydraulic inlet port and said hydraulic outlet port when said secondary piston is displaced from its biased position.
 3. A device according to claim 1 wherein a chamber is defined by each end of said secondary piston and the ends of said second cylindrical recess, said chambers communicating with each other via a constriction orifice and passageway through said secondary piston.
 4. Device according to claim 1 wherein check valves are placed in the at least third hydraulic inlet port.
 5. Device according to claim 1 wherein the spring biasing means is pretensionable by means of a screw device and is placed in a chamber of the cylinder which is connectable to the fluid recipient. 